The field of this invention relates to landing collars for wiper plugs used in cementing operations and more particularly to the construction thereof, using composite materials as well as the mounting technique in casing.
Landing collars are used as an accessory inside liner casing strings for cementing operations. The landing collars must be removed at the conclusion of the cementing job, usually by drilling it out. Since drilling out takes time, prior solutions have emphasized the use of relatively soft metals such as aluminum. Aluminum still presented too much resistance to drilling out. More recently, U.S. Pat. No. 6,079,496 addressed the problem of shocking the formation when landing wiper plugs on landing collars. Although the focus of this patent was in shock reduction, it also suggested that drillability of landing collars could be improved by using non-metallic components. It further suggested use of engineering grade plastics, epoxies, or phenolics for many of the landing collar components. It further suggested use of a ceramic ball seat in combination with a non-metallic ball. This patent, which is being reissued to add claims to these features, did not detail construction techniques, which would allow bump pressure differentials of 10,000 PSI or more. It did not illustrate a mounting technique compatible with such high-pressure differentials.
One of the objectives of the present invention is to provide a landing collar that can be securely mounted in a manner which will eliminate or minimize leakage around its connection to the liner string while at the same time the landing collar possesses the structural strength to withstand bump pressures in excess of 10,000 PSI when the wiper plug lands. At the same time, the landing collar can effectively hold the wiper plug against rotation during drill out. Finally, the unique construction combines the feature of rapid drill out. Those skilled in the art will more readily understand these and other advantages of the present invention by a review of the description of the preferred embodiment, which appears below.
A composite landing collar is disclosed which is preferably adhesive bonded to the liner string using a high temperature epoxy. The spacing during bonding is maintained within dimensional limits using spacers. The body features a bi-directional material, with an appropriate ratio in the warp and fills directions, for about a quarter of the wall thickness. A unidirectional material with the fibers axially aligned aids in reduction of thermal stresses in the thick wall during curing, as well as reducing shear stress concentration along the adhesive bonding interface.